Restricting surface area for snapping to other objects
This is something that I am working on as well, so I might as well share what I have learned.
A nice way to isolate the target area in the edit mode is to hide the geometry you don't want to be affected by an operation.
You can then safely work only on the area you want, without affecting any of the other vertices.
Other notes:
-make sure to toggle proportional editing off; this is an extremely powerful function
-snapping can be used (the magnet icon) to connect edges or align by increments
-use bridge connect tool